Ion implantation has been utilized for some time in the manufacture of NPN transistors. Typically, both the P base region and the N emitter region may be formed by the ion implantation method. Ion implantation causes damage during the implantation of the doping ions. This is normally cured by an annealing step. However, there are dislocation faults which do remain even after the annealing of the structure having the doping ions.
Methods for improving the direct ion implantation of bases and emitters directly into the monocrystalline silicon device region have been developed. U.S. Pat. No. 3,460,007 to Scott describes a method for forming a P-N junction wherein N doped polycrystalline silicon is deposited in situ on the surface of the monocrystalline silicon structure. The structure is subsequently heated to drive the N type conductivity ions into the surface of the monocrystalline silicon to form the N region. A further modification described in the publication by Graul et al., IEEE Journal of Solid State Circuits, Vol. SC-11, No. 4, August 1976, pp. 491-493, discusses a method for forming an emitter for an NPN transistor. In that method, an undoped polycrystalline silicon layer is deposited upon the surface of a monocrystalline silicon substrate. The polycrystalline silicon layer is then ion implanted with an N type ion, such as arsenic. The arsenic is then driven into the surface of the monocrystalline silicon to form the emitter region. U.S. Pat. No. 4,190,466 to A. Bhattacharyya et al. describes a method for using two layers of polycrystalline silicon as the dopant sources for diffusing boron and arsenic in consecutive operations to form the base and emitter regions, respectively of an NPN device.
K. Takahashi et al., U.S. Pat. Nos. 4,226,650 and 4,263,067 describe methods for forming PN regions in a monocrystalline semiconductor body by means of driving appropriate impurities from a silicon dioxide film. This process involves formation of a silicon dioxide film on the surface of the monocrystalline silicon body, the ion implantation of, for example, boron and arsenic impurities into the silicon dioxide film and heating the structure to diffuse the boron and arsenic simultaneously from the doped silicon dioxide layer to form the P type base layer and PN junction. The I. T. Ho et al. IBM Technical Disclosure Bulletin, Vol. 20, No. 1, June 1977, pp. 146-148 describes the formation of a PN junction useful in a charge-coupled device type storage element. The process utilizes polycrystalline silicon layer which has been formed on a monocrystalline silicon substrate. The polycrystalline silicon layer has boron and arsenic impurities therein. Upon heating the structure the boron which has a diffusion coefficient ten times higher than that of arsenic will diffuse more rapidly into the monocrystalline silicon to form a P layer region which surrounds the arsenic N region of the resulting structure.